code: def test_inverse_transform_HaveNanInTrainAndHandleMissingReturnNan_ExpectReturnedWithNan(
      self,
  ):
      train = pd.DataFrame({"city": ["chicago", np.nan]})
  
      enc = encoders.OneHotEncoder(
          handle_missing="return_nan", handle_unknown="value"
      )
      result = enc.fit_transform(train)
      original = enc.inverse_transform(result)
  
      pd.testing.assert_frame_equal(train, original)
  
imports: import pandas
  from unittest import TestCase
  import numpy
  import tests.helpers
  import category_encoders
label_desc: Use image node_id 20 for calling the TestOneHotEncoderTestCase obj's underlying member method code with example usage: obj.test_inverse_transform_HaveNanInTrainAndHandleMissingReturnNan_ExpectReturnedWithNan() without return types